The invention relates to an image projection device comprising an illumination system having a lamp for supplying an illumination beam, at least one image display panel having a periodical structure of pixels for modulating the illumination beam in accordance with an image to be projected to a signal beam, and a projection lens system for projecting the image on an image projection screen.
The image projection screens which are used for said image projection devices are provided, at least at the side facing the audience room, with a periodical light-scattering structure, for example a periodical structure of elongate lenses extending in a direction which also occurs in the structure of the image display panel and whose dimensions are of the same order as the dimensions of the periodical structure of the pixels of the image display panel projected on the screen. Due to interference between the two periodical structures of the same order, disturbing Moire patterns are produced upon projection on the screen. The extent of Moire interference, in other words, the modulation depth of the interference pattern is dependent on the ratio between the pitch of the periodical light-scattering structure of the screen and the pitch of the pixels of the image display panel, on the size of the active portion within a pixel and on the configuration of the pixels in the panel. The configuration may comprise rows of pixels, with the pixels of two adjacent rows being exactly subjacent to each other. This is referred to as the orthogonal structure. In another configuration the pixels of two adjacent rows are offset by half a pitch with respect to each other. This is referred to as the delta structure.
An image projection device of the type described in the preamble, in which such Moire interference is reduced, is known from the English-language Abstract of JP-A 4-125536. In the image projection device described in this Abstract a plane-parallel plate is arranged in the light path between the liquid crystal display panel and the projection lens in the beam at an angle with respect to the horizontal and vertical axes of the image display panel, such that the periodical structure of the panel is sharply imaged in one direction only, while the image in the other direction in which Moire interference occurs is defocused. However, this has the drawback that the imaging quality of the image to be projected itself will be worse in one direction.